I have successfully had male guinea pigs of different ages bond well, i find it's all down to personality, if you new piggy is laid back, you get another laid back boy to keep the peace, if you have a dominant one, getting a male who's submissive and won't challenge the other, allows the other to not feel threatened, and they generally get on quite well..
I have two males who constantly hump each other, never fight, just 'hump'.. quite a show when they're out:giggle:
I also find Peruvians are pretty laid back, both the piggies i've had took day to day life in their stride..
Abby's.. well they're wired:giggle:
Smooth coats.. I've had allsorts.. down right bad tempered :devil: to real softies:wub: I put them in the 'grey' area as I found their personalities really varied:balanced: